Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 122348

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
648 PM EST Thu Jan 12 2017

A cold front will approach the region from the northwest
through Friday and stall over the area by Saturday morning. A cool
wedge of high pressure will nose into the region from the north just
behind the front through late Saturday. The front will retreat north
as a warm front on Sunday. High pressure will then strengthen over
the southeast early next week to keep temperatures above average.


As of 645PM EST Thursday:  Prefrontal stratocu continues to work
into the region from the west as a cold front moves across the TN
Valley.  As such, a few sites across NE GA, SW NC, and the western
Upstate are reporting 4-6kft ceilings, thus opted to increase sky
cover a bit for these regions, while mainly high cirrus prevails
elsewhere.  Winds have calmed from earlier gusting as the BL begins
to decouple, therefore did allow fcst to continue with previous
trends.  Otherwise, no sig changes needed/made with this update.

As of 2:00pm Thurs.:  Temperatures are warming nicely around the
region and had to raise today`s high temps several degrees to
catch up with observations.

Continental frontal boundary is well off to the northeast of the
region, across western KY/TN, but will gradually move towards the
Southern Appalachians and will support some scattered precip over
the mountains ahead and behind it.  Front weakens and passes through
the region by Friday afternoon, but has little affect on boundary
layer moisture, temperatures, or dewpoints, with some light,
widely scattered showers lingering through the day on Friday.
Upper pattern transitions from southwesterly flow to zonal.
Ridge of surface high pressure behind the front/surface trough
will begin the process of creating a CAD/wedge boundary that will
move towards the area late Friday.  As Friday will be ahead of
CAD effects, afternoon highs will again be quite warm with highs
in Piedmont areas in the low 70s (which compares with records for
this time of year in the mid to upper 70s).

With some southwesterly surface flow, boundary layer moisture
will continue to gradually advance with dewpoints rising a few
more degrees.  Improved low-level moisture will give some chance
for patchy fog Friday morning, which will clear quickly after
daybreak with BL warming.  850mb flow of 25 to 30kts is creating
some gusty winds today that will relax after sunset this evening.
850mb flow weakens considerably with the FROPA early on Friday,
and significant gusts are not anticipated for Friday.


As of 215 PM EST Thursday: A stalling frontal boundary will likely
be draped over the heart of the forecast area around the start of
the short term period Friday evening. The boundary will likely get a
southward push through daybreak Saturday as a 1040+ mb surface high
center builds over to the north from the Great Lakes to New England.
Upglide over the shallow cold air damming layer looks rather weak,
but the more aggressive southwest surge of the wedge on the GFS will
be favored given the parent high strength and location. Any weak
upglide over the wedge layer will gradually diminish through
Satruday as 850 mb flow adjusts more westerly over time. QPF Friday
night through Saturday should be rather light, with local quarter
inch plus amounts mainly over the NC foothills and the southwest
mountains where the precipitation could be more showery in nature.
Anticipate rather small diurnal temperature variations Friday night
through Saturday night in locations affected by cold air damming.

Meanwhile, a flat upper level ridge will remain in place over the
southeastern U.S. through the weekend. Continued weak downsloping
and some deeper drying working in will diminish the cold air damming
through Sunday - with temperatures likely rebounding into the 60s
across the foothills, piedmont, and lower mountain valleys. Any
lingering late week shower chances should be confined mainly to
locations north of the Interstate 40 corridor, closer to the
retreating wedge/warm front.


As of 225 PM Thursday, an upper ridge builds over the eastern CONUS
Monday. The ridge axis slides east to the coast Tuesday as the first
of a series of short waves tops the ridge. At the surface, high
pressure builds into the area in a damming pattern Monday. The high
slides east on Tuesday in the progressive pattern. Rain chances
remain low but not none with weak upglide and upslope flow over the
area. The air mass is quite warm despite the damming pattern. Lows
will be 15 to 20 degrees above normal each morning, with highs 5 to
10 above normal Monday and 10 to 15 above normal Tuesday.

Another short wave tops the ridge Wednesday as it continues to move
east. Some weak short wave energy may move over the area during this
time. A stronger short wave moves into the area from the SW on
Thursday. The Wednesday short wave moves a surface low to our north
but drags a cold front toward the area. A secondary low pressure
wave forms along the front with the SW short wave. This helps drag
the front into the area on Thursday. With the low level flow
remaining generally southerly, there will be quite a bit of
moisture, upglide, and upslope flow over the area. This leads to
slowly increasing precip chances, with the highest PoP on Wednesday
night and Thursday. Bulk shear will increase significantly with the
front, but instability remains minimal at best. The operational
guidance does bring a CAPE of 200 or so into the area. However the
ensemble mean is less. Therefore, severe weather cannot be ruled out
but uncertainty remains high enough to keep out of the HWO attm.
Highs will be 10 to 20 degrees above normal each day with lows 15 to
20 above normal each morning.


At KCLT/KHKY and the SC Sites:  High pressure to prevail through the
vast majority of the taf cycle, before a backdoor front wedges into
the region late on Friday.  VFR initially, with chances of MVFR/IFR
visb restrictions increasing near daybreak as td depressions
minimize leading to light ground fog.  Thus all sites feature
4-5sm visb with the exception of KHKY where 2-3sm is included.
Moisture in the llvs will warrant at least a few/sct 040-060 mention
through the night, thinning a bit after daybreak, however likely
returning into late morning to early afternoon as mixing increases.
Winds overnight are to remain light and sly, increasing a bit with
mixing as heating builds on Friday, with sharp nw/ne veering favored
at KHKY and KCLT as the wedge boundary intrudes.  All other sites
to remain sly/swly through 00z.  Also included vcsh/prob30 for shra
at KHKY as upglide precipitation is expected before periods end.

At KAVL:  Moisture associated with a TN valley frontal boundary
will affect KAVL later in the taf period, thus warranting vcsh
and prob30 mention for shra.  Otherwise, trends similar to that
of the sites above, however expecting more dense sky cover, lower
MVFR/IFR cigs/visb overnight in the mtn valleys, lifting to high
MVFR or low VFR after sunrise Friday.  Winds will initialize swly,
however veer nwly overnight.

Outlook: Cool high pressure ridges down the East Coast over the
weekend, bringing chances for precipitation and restrictions.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     High 100%     High  83%     High 100%
KGSP       High 100%     High 100%     Med   78%     High 100%
KAVL       High 100%     Med   60%     Low   31%     Med   62%
KHKY       High 100%     High 100%     Med   61%     High 100%
KGMU       High 100%     High 100%     Med   78%     High 100%
KAND       High 100%     High 100%     Low   38%     High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:




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